Inj and Ign voltages drops

[acca]

Hello
I have a question about Inj and ign voltages logging, as one can see in the picture, those voltages are not constant.
Is that normal please ?

image ign inj volt.PNG (53.14 KiB) Viewed 8672 times

[Stephen Dean]

Hi,

I wouldn't be concerned about the way that the data traces look, as these can be changed a large amount based on the sample rate of the channel.

This is my ignition voltages logged at 100hz when the engine is idling at ~1000rpm. The missing Cyl 4 is because the event happened between sampling points, if I logged the channel at a higher rate I would have most likely have gotten these captured.

Ign Voltages.PNG (17.22 KiB) Viewed 8657 times

This is the same data with differing filters applied.

Ign Voltages Filtered.PNG (14.35 KiB) Viewed 8657 times

I have filtered Cyl 1 to the equivalent of 1hz logging, Cyl 2 to 2Hz, Cyl 3 to 5Hx and Cyl 4 to 10Hz.

[acca]

Ok, so it's hidden by sample rate !
Thanks

[David Ferguson]

Nyquist to the rescue.

https://whatis.techtarget.com/definitio ... st-Theorem

Basically if you want to make sure you capture the details of a signal that can change at frequency X, you have to sample at 2X the frequency.

The diagnostic voltages for Injectors and Ignitions can really only be used to determine if they seem to be stuck high or stuck low, as you would need to sample at 20khz in order to see signals to resolved to the nearest .1ms